Filament support for tungsten-iodine incandescent lamps



July 25, 1967 w J. M LINTIC 3,333,139

FILAMENT SUPPORT FOR TUNGSTEN IODINE INCANDESCENT LAMPS Filed April 25, 1965 Fig.1.

Fig. 2.

WILLIAM JAMES MCLINTIC INVENTOR ATTORNEY United States Patent 3,333,139 FILAMENT SUPPORT FOR TUNGSTEN-IODINE INCANDESCENT LAMPS William James McLintic, London, England, assignor to Thorn Electrical Industries Limited, London, England, a British company Filed Apr. 25, 1963, Ser. No. 275,689 Claims priority, application Great Britain, Apr.

16,070/ 62 5 Claims. (Cl. 313-274) The present invention relates to filament supports for incandescent lamps and more particularly to filament supports for tungsten-iodine lamps.

In tungsten-iodine lamps, the filament which is generally in the form of a long spiral is surrounded by an envelope of quartz or other transparent vitreous material which is also long and narrow in order to obtain the best operating conditions for the lamp. If the filament voltage is increased and the power rating (that is wattage) is kept constant, the length of the tungsten wire used to form the filament increases while its diameter decreases, hence the finished filament tends to lose its rigidity and has to be supported at some point other than at its ends.

In the case of single coil filaments this may be done by means of a series of single turn tungsten wire rings of diameter equal to the internal diameter of the envelope of the lamp. One end of the wire of each ring extends radially inwards and is curled tightly round the coiled filament. The rings fit into the envelope and spring against the wall, holding the filament in position.

This kind of support is ill suited for use in the case of coiled coil filaments because the pitch of the secondary coil is so large that fine wire will not hold it bodily and the support wire has to encircle the primary coil at a point which is necessary oif the axis of the filament and is therefore asymmetrically disposed relative to the weight of the filament. Moreover the rigidity of the coiled coil filament is so much less than that of a single coil filament that one single turn ring of wire will not maintain it in its correct position under conditions of vibration or shock. A variant of this utilises thicker support rings which form part of the filament electrically. Thus each ring has two ends directed radically inwardly and the ends of filament sections to either side of the ring are pushed over these inwardly directed ends. This arrangement is particularly susceptible to shock, particularly shock along the axis.

Another method of supporting a coiled coil filament is to attach the filament to a spring having several turns on either side of the point of contact of the spring and the filament. The diameter of the spring is roughly equal to the internal diameter of the envelope, the latter being thus used to locate the spring support axialy. The turns are wound with a very open pitch and extend along the length of the filament. This method has the disadvantage that the wire must be fine to avoid interference with the light output from the filament, and it is therefore difiicult to form and maintain the satisfactory spiral shape needed to obtain the required efiective supporting.

It is also known that a tungsten wire cannot pass through a quartz and similar high silica content glass and be satisfactorily hermetically sealed thereto.

The present invention provides a satisfactory support which has no considerable practical disadvantages.

According to the present invention there is provided an incandescent lamp comprising an envelope of quartz or other transparent vitreous material and a filament inside the envelope, wherein the filament is supported, at a point intermediate the ends thereof, by a support wire, one end of the wire being enclosed in the wall of the envelope.

There is also provided a method of making an in- "ice candescent electric lamp, wherein the filament with a support wire attached thereto is positioned within the envelope, one end of the wire extending into a tube through which the lamp is then exhausted, after which the tube is sealed oii so as to enclose the said end of the wire totally within the remains of the tube.

The other end of the wire may be extended so that it butts against the opposite wall of the envelope to that enclosing the one end of the wire. In this way more support is obtained. Furthermore the wire and filament may be sited in the tube with greater accuracy than if the wire was terminated immediately after it contacted the filament. i

In manufacturing a lamp according to the invention the support wire is attached to the filament before it is mounted in the envelope. The filament is supported and mounted in the usual manner at its ends for example by solid wire plugs and molybdenum strips. The one end of the support wire is subsequently totally enclosed in the wall of the envelope. Advantage may be taken of the fact that an exhaust tube is appended to the envelope, through which the lamp is exhausted. If this tube is provided at the point where the support wire is sealed into the envelope, then the one end of the wire may be enclosed in the remains of the exhaust tube when this is sealed off after exhaustion of the lamp. Care must be taken to ensure that the wire is sealed into the wall in such a position that the filament is supported in its prescribed position. For instance it is sometimes difiicult to prevent the remains of the exhaust tube from retracting inwards under the influence of atmospheric pressure (which is greater than that of the gas filling) during the sealing off process, thereby moving the support wire and the filament. To combat this tendency, the other end of the wire may be extended so that when the filament is in its correct position, the other end of the wire butts against the opposite interior wall of the envelope to that in which the one end of the wire is enclosed, thus preventing the one end from retracting into the envelope.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a diagram of one embodiment of the invention before the support wire has been sealed into the envelope.

FIG. 2 is a diagram of one end of the support wire sealed into the envelope.

FIG. 3 is a diagram of a further embodiment of the invention.

A tungsten-iodine lamp comprises an envelope 10 (FIG. 1) enclosing a coiled coil filament 12. The primary turns of the filament are too fine to be shown in this figure. The filament 12 is mounted at its ends in the ends of the envelope 10 in the usual manner. In the centre of the envelope, there is an exhaust tube 14. A wire 16 is attached to the filament 12 and one end 18 of the wire 16 projects a little way into the tube 14. For example, in a lamp whose envelope is 3 /2 ems. long and 1% ems. in diameter the end 18 could project about 2 /2 mm. into the exhaust tube 14. After the lamp has been exhausted, the tip 18 is totally enclosed in the remains 20 of the exhaust tube 14 when the tube 14 is sealed 01f (FIG. 2), so that the end 18 of the wire is firmly fixed to the envelope.

The point at which the wire 16 is attached to the filament 12 is approximately midway along the secondary coil of the filament 12, on the part of the primary coil nearest the exhaust tube 14.

The other end 22 of the wire 16 may be terminated immediately after the point where it is attached to the filament 12 (FIG. 1) or it may be extended to butt r 3 against the wall of the envelope opposite to the exhaust tube 14 (FIG. 3).

The end 18 of the wire tends to retract towards the interior of the envelope during the sealing off process, thereby making it difficult to position accurately the filament 12. If the wire 16 is extended as in FIG. 3, the wire cannot move in this way and so the filament can be more easily positioned. Furthermore, the support so obtained is more rigid than if the wire 16 was terminated as in FIG. 1.

It is essential that the end of the wire should be totally enclosed, as shown in FIG. 2, and should not protude at all through the tube wall. Otherwise a satisfactory hermetic seal cannot be produced when the support wire is of tungsten or similar refractory metal.

A plurality of support wires 16 may be used. A plurality of appendages similar to the exhaust tube 14 may be provided, each support wire 16 being associated with one appendage. One end of each wire 16 is then enclosed in the remains of its respective appendage, in the way already described, before the lamp is exhausted.

The support wires may be spaced at regular intervals along the axis of the filament.

This method of support may be used for single coil filaments or coiled coil filaments.

In the case of coiled coil filaments, the secondary winding may be interrupted at the point of contact with the supports in order to lessen the risk of accidental shorting of secondary turns of the filament to the support wire.

Other shapes of support can, of course, be used in place of a straight wire support.

I claim:

1. An incandescent lamp comprising a transparent vitreous envelope, a coiled filament inside the envelope, a support wire, the filament being supported at a point intermediate the ends thereof by the support wire, an

end of the support wire being totally enclosed in the wall of the envelope.

2. A tungsten-iodine lamp comprising a cylindrical transparent vitreous envelope, a coiled tungsten filament disposed inside the envelope, with its axis substantially along the axis of the cylindrical envelope, terminals at the ends of the envelope, the ends of the filament being fixed to the terminals, a support wire, the filament being supported at a point intermediate the ends thereof by the support wire, one end of the support wire being totally enclosed in the wall of the envelope.

3. A lamp according to claim 2, wherein the support wire is substantially straight and is disposed approximately on a diameter of the cylindrical envelope.

4. An incandescent lamp comprising a transparent vitreous envelope, a coiled filament inside the envelope, a support wire, the filament being supported at a point intermediate the ends thereof by the support wire, one end of the support wire being totally enclosed in the wall of the envelope, the other end of the support wire butting against the interior of the envelope.

5. An incandescent lamp comprising a transparent.

vitreous envelope having a sealed-ofi? exhaust tube, a filament inside the envelope, a support wire, the filament being supported at a point intermediate the ends thereof by the support wire, one end ofthe support wire being totally enclosed in the sealed-off exhaust tube.

References Cited UNITED STATES PATENTS 960,962 6/1910 Kuzel 313274 1,107,650 8/1914 Beuttell 313273 2,894,166 7/1959 Mohn 313-272 3,093,769 6/1963 Kuhl et al. 313274 3,173,051 3/1965 Berlinghof et al. 313-274 JOHN W. HUCKERT, Primary Examiner. A. 1. JAMES, Assistant Examiner. 

5. AN INCANDESCENT LAMP COMPRISING A TRANSPARENT VITREOUS ENVELOPE HAVING A SEALED-OFF EXHAUST TUBE, A FILAMENT INSIDE THE ENVELOPE, A SUPPORT WIRE, THE FILAMENT BEING SUPPORTED AT A POINT INTERMEDIATE THE ENDS THEREOF BY THE SUPPORT WIRE, ONE END OF THE SUPPORT WIRE BEING TOTALLY ENCLOSED IN THE SEALED-OFF EXHAUST TUBE. 